Field of Invention
The present invention relates to a field of rare earth permanent magnet, and more particularly to a high-performance NdFeB rare earth permanent magnet with composite main phase and a manufacturing method thereof.
Description of Related Arts
NdFeB rare earth permanent magnets are more and more widely used due to excellent magnetic properties thereof. For example, the NdFeB rare earth permanent magnets are widely used in medical nuclear magnetic resonance imaging, computer hard disk drivers, stereos, cell phones, etc. With the requirements of energy efficiency and low-carbon economy, the NdFeB rare earth permanent magnets are also used in fields such as automobile parts, household appliances, energy conservation and control motors, hybrid cars and wind power.
In 1983, Japanese patents No. 1,622,492 and No. 2,137,496 firstly disclosed NdFeB rare earth permanent magnets invented by Japanese Sumitomo Metals Industries, Ltd., which disclose features, components and manufacturing methods of the NdFeB rare earth permanent magnets, and confirm that a main phase is a Nd2Fe14B phase and a grain boundary phase comprises a rich Nd phase, a rich B phase and rare earth oxides. NdFeB rare earth permanent magnets are widely used because of excellent magnetic properties, and are called the king of permanent magnets. U.S. Pat. No. 5,645,651, authorized in 1997, further disclosed adding Co and the main phase having a square structure.
With the wide application of the NdFeB rare earth permanent magnets, rare earth becomes more and more rare. Especially, shortage of heavy rare earth element resource is significant, so that price of the rare earth is continuously increasing. Therefore, after a lot of exploring, double-alloy technology, metal infiltration technology, grain boundary improving or recombining technology, etc. appear. Chinese patent CN101521069B discloses a method of manufacturing NdFeB doped with heavy rare earth hydride nano-particles, wherein an alloy flake is firstly manufactured with strip casting technology, then powder is formed by hydrogen decrepitating and jet milling, the above power is mixed with heavy rare earth hydride nano-particles formed by physical vapor deposition technology, and then the NdFeB magnet is manufactured through conventional processes such as magnetic field pressing and sintering. Although the Chinese patent discloses a method to enhance coercivity of the magnet, there is problem for mass production.
Chinese patent CN1688000 discloses a method for improving coercivity of the sintered NdFeB by adding nanometer oxides in the grain boundary phase. The method is an improvement of the double-alloy method. Firstly, the main phase alloy and the grain boundary phase alloy respectively utilize the casting process to manufacture NdFeB alloy ingots, or utilize the strip casting flake process to manufacture strip casting alloy flakes, then respectively utilize the hydrogen decrepitating method or the crusher for decrepitating, then powder with jet milling to manufacture powder with a size of 2-10 μm; then add 2-20% dispersed nanometer oxides and 1-10% anti-oxidants by weight into the grain boundary phase powder and evenly mix in the mixer; then mix the grain boundary phase alloy powder doped with the nanometer oxides with the main phase alloy powder, wherein the grain boundary phase alloy powder is 1-20% by weight, and simultaneously, add 0.5-5% gasoline, evenly mix in the mixer for manufacturing mixture powder; press the mixture powder at the magnetic field of 1.2-2.0 T, then sintering for manufacturing the NdFeB magnet. The core technique of the present invention is: the grain boundary phase is modified by evenly distributing the nanometer oxides in the grain boundary phase to improve the coercivity of the NdFeB magnet; the main phase and the grain boundary phase are respectively molten, powdered and mixed repeatedly in the present invention. The NdFeB fine powder is very easy to be oxidized, so the process is complex and not easy to be controlled. Furthermore, when the main phase alloy is molten, due to low content of rare earth, a composition of the main phase alloy is close to that of Nd2Fe14B phase, it is easy to produce α-Fe so that the remanence is reduced; easy to produce the main phase while melting the grain boundary phase so that the coercivity is affected. Furthermore, due to large surface area of the nanometer oxide, it is dangerous to explode while transporting and using. The nanometer oxide has difficult manufacturing process and high cost, which affects the application of NdFeB.